The present subject matter generally concerns improved component design for decoupling capacitors that generally results in devices characterized by relatively low cost, low inductance and controllable Equivalent Series Resistance (ESR).
As switching speeds increase and pulse rise times decrease in electronic circuit applications, the need to reduce inductance becomes a serious limitation for improved system performance. Even the decoupling capacitors, which act as a local energy source, can generate unacceptable voltage spikes, as reflected by the calculation of V=L (di/dt). Thus, in high speed circuits where di/dt can be quite large, the size of the potential voltage spikes can only be reduced by reducing the inductance value L.
The prior art includes several strategies for reducing equivalent series inductance, or ESL, of chip capacitors compared to standard multilayer chip capacitors. A first exemplary strategy involves reverse geometry termination, such as employed in low inductance chip capacitor (LICC) designs such as manufactured and sold by AVX Corporation. In LICCs, electrodes are terminated on the long side of a chip instead of the short side. Since the total inductance of a chip capacitor is determined in part by its length to width ratio, LICC reverse geometry termination results in a reduction in inductance by as much as a factor of six from conventional MLC chips.
Interdigitated capacitors (IDCs) incorporate a second known strategy for reducing capacitor inductance. IDCs incorporate electrodes having a main portion and multiple tab portions that connect to respective terminations formed on the capacitor periphery. Multiple such terminations can help reduce the parasitic inductance of a device. Examples of interdigitated capacitors are disclosed in U.S. Pat. No. 6,243,253 (DuPre et al.)
A still further known technology utilized for reduction in capacitor inductance involves designing alternative current paths to minimize the mutual inductance factor of capacitor electrodes. A low inductance chip array product, such as manufactured and sold by AVX Corporation under the LICA® brand, minimizes mutual inductance by configuring a ball grid array multilayer capacitor such that the charging current flowing out of a positive plate returns in the opposite direction along an adjacent negative plate. Utilization of LICA® brand technology achieves low inductance values by low aspect ratio of the electrodes, an arrangement of electrode tabs so as to cancel inductance and vertical aspect of the electrodes to the mounting surface.
Additional references that incorporate adjacent electrodes having reverse current paths used to minimize inductance include U.S. Published Patent Application No. 2005/0047059 (Togashi et al.) and U.S. Pat. No. 6,292,351 (Ahiko et al.). Both such references also utilize a vertical aspect of electrodes relative to a mounting surface. Additional references that disclose electrodes for use in a vertically-oriented position include U.S. Pat. No. 5,517,385 (Galvagni et al.); U.S. Pat. No. 4,831,494 (Arnold et al.); and U.S. Pat. No. 6,885,544 (Kim et al.).
A known reference that discloses features aimed to reduce inductance in an integrated circuit package that includes a capacitive device is U.S. Pat. No. 6,483,692 (Figueroa et al.). Such reference recognizes that inductance relates to circuit board “loop area” or the electrical distance (or span) that current must follow. It is desirable in Figeuroa et al. to minimize such loop area, thus reducing the inductance levels. Extended surface lands are also provided in Figueroa et al., providing a larger surface area that is said to result in more reliable connections characterized by reduced inductance and resistance levels.
U.S. Pat. No. 6,661,640 (Togashi) also discloses features for reducing ESL of a decoupling capacitor by maximizing the surface area of device terminations. U.S. Pat. No. 6,917,510 (Prymak) discloses a capacitor embodiment with terminal extensions formed to result in a narrow gap between the electrodes. The end electrodes of U.S. Pat. No. 6,822,847 (Devoe et al.) also cover all but a thin separation line at a central portion of the capacitor body. U.S. Pat. No. 7,054,136 (Ritter et al.) discloses a low inductance controlled equivalent series resistance multilayer ceramic capacitor providing controlled amounts of resistive material in the terminations.
Still further known references that include features for reducing component inductance correspond to U.S. Pat. No. 6,757,152 (Galvagni et al.) and U.S. Pat. No. 6,606,237 (Naito et al.), in which conductive vias are utilized to form generally low inductance connections to upper electrodes in a multilayer capacitor.
Additional background references that may address certain aspects of low-inductance multilayer electronic devices include U.S. Pat. No. 6,576,497 (Ahiko et al.) and U.S. Pat. No. 3,444,436 (Coda) as well as U.S. Published Patent Application No. 2004/0184202 (Togashi et al.).
The disclosures of all the foregoing United States patents and published patent applications are hereby fully incorporated into this application for all purposes by virtue of present reference thereto.
While various aspects and alternative features are known in the field of multilayer electronic components and related methods for manufacture, no one design has emerged that generally addresses all of the issues as discussed herein.